The 3rd Generation Partnership Project (3GPP) is responsible for the standardization of the Universal Mobile Telecommunication System (UMTS) and Long Term Evolution (LTE). The 3GPP work on LTE is also referred to as Evolved Universal Terrestrial Access Network (E-UTRAN). LTE is a technology for realizing high-speed packet-based communication that can reach high data rates both in the downlink and in the uplink, and is a next generation mobile communication system relative to UMTS.
In a wireless communications network, such as an LTE or UMTS network, radio access is provided to wireless devices by one or more radio base stations, also referred to herein as a “network node” or “radio network node”. A base station is associated with one or more antennas which are used for the transmission and reception of one or more cells that are served by the base station. The base station and its associated antennas are sometimes referred to as a “base station site”, “cell site”, or simply “site” in the following. In the context of this disclosure, each cell is associated with a physical cell identity (PCI), which is at least locally unique, i.e. it is unique among the cells served by a certain base station and its neighbouring cells. The cell identity is broadcast within the cell, allowing wireless devices to identify the cell. In a typical, non-limiting scenario, a base station is associated with three sector antennas. In one configuration, each sector antenna forms a separate sector cell having a separate PCI. In an alternative configuration, all three antennas are utilized for transmitting a macro cell or “omni cell” having one single PCI. Intermediate configurations may exist, e.g. with one antenna transmitting a sector cell and the remaining two antennas transmitting a “multi-sector cell” covering two sectors. Throughout this disclosure, the term “multi-sector cell” or “multi-cell” will be used to refer to configurations where two or more sectors are merged into a single cell. It should be appreciated that the presence of a multi-sector cell does not exclude that additional sector cells, or even additional multi-sector cells, may be served by the same base station. The expression “omni cell” generally refers to a scenario where all sectors of a base station are merged into one cell. It should be appreciated that an omni cell is a special case of a multi-sector cell, and that examples and embodiments set forth herein referring to “omni cells” are also applicable more generally to multi-sector cells unless stated otherwise.
In a UMTS radio access network (RAN), the network node providing radio base station functionality is referred to as a NodeB. The NodeB is a logical node handling the transmission and reception of a set of cells. A Radio Network Controller (RNC) manages radio resources and provides control functionality for one or more NodeBs.
In an LTE RAN, the radio base station node is referred to as an eNodeB, and this node also handles the additional control functionality provided by the RNC in UMTS.
To meet the ever increasing demand for higher capacity in wireless networks, one approach is to deploy heterogeneous networks (HetNets), i.e. a network containing base stations operating with different transmission power. Base stations operating with high transmission power are commonly denoted macro base stations (or macro sites), and base stations operating with lower transmission power may be referred to as e.g. micro, pico, or femto base stations, or more generally as low power nodes. In such heterogeneous network deployments, the macro base stations can be said to form a “coverage layer”, i.e. they provide a layer of macro cells having wide coverage areas. The low power nodes form a “capacity layer”, i.e. a layer of smaller cells providing increased capacity in smaller areas within the macro cells, where high traffic levels are anticipated.
It is generally desirable to decrease energy consumption of radio access networks, both for environmental reasons and to save operational costs. Energy savings may be achieved at various different levels, e.g. by using more efficient components in the base stations, by improving the resource usage of individual radio links, or by improved network deployment strategies. Mechanisms for decreasing energy consumption have been considered in the Energy Aware Radio and neTwork tecHnologies (EARTH) project.
At a certain base station site, the radio resource need and the desired focus of network coverage may typically vary over time. Hence, some energy saving techniques are aimed at adapting to daily and local variations of traffic in various ways, for example by allowing a base station to go into sleep mode (discontinuous transmission, DTX) during idle periods. Another possibility is to completely deactivate certain cells or cell sites during a certain time period, while configuring other cells to take over the coverage. For instance, low power nodes such as pico cells might be turned off during off-peak hours.
A further way of reducing energy consumption based on traffic variations over time is to perform sector-to-omni cell reconfiguration within a base station site, as discussed in the EARTH deliverable D6.4, which is available electronically at https://bscw.ictearth.eu/pub/bscw.cgi/d49431/EARTH_WP6_D6.4.pdf. As described therein, in off-peak hours, one or more sectors may be switched off, and the antenna pattern of the remaining sector is changed to omni-directional to maintain coverage in the silent sector(s). The EARTH deliverable considers this as a slow energy saving method that operates on a time scale of approximately 12 hours. Typically, a site would be configured for omni coverage during night time and sector coverage during day time.
Multi-antenna techniques may be applied in UMTS as well as LTE in order to improve system performance. For example, Multiple-Input-Multiple-Output (MIMO) refers to the use of multiple antennas at both the transmitter and receiver side. Examples of different MIMO techniques are precoding (e.g. beamforming), spatial multiplexing, and transmit diversity. MIMO muting, or antenna muting, is an energy saving technique that is discussed in the EARTH deliverable mentioned above. The preferred method to enable antenna muting will be referred to as “antenna port merging” in the following disclosure. Antenna muting is considered to be a fast energy saving method applicable on e.g. a timescale of seconds. The idea is to activate or deactivate antennas based on the current amount of traffic. Thus, at low load, traffic can be handled by a single antenna and the other antennas are then muted. This may save energy because each antenna is usually served by a separate power amplifier. Antenna muting may be implemented in several ways. One possibility is to set the output power for the muted antenna ports to zero, i.e. no signals will be transmitted on these antenna ports. In a second (preferred) alternative, signals intended for all the antenna ports are added (i.e. the antenna ports are “merged”) and then transmitted via one single physical antenna. In a third alternative, assuming a system with four transmit antennas, i.e. four antenna ports, the first and second antenna ports may be merged whereas no signal is transmitted on the third and fourth ports, i.e. the output power for the third and fourth ports are set to zero. Additional antennas may be activated as the load in the cell increases. The EARTH deliverable proposes applying fast antenna muting in relatively dense deployed networks with good coverage.